1. Field of the Invention
The present invention relates to a method for excavating the ground or drilling a hole in the ground through utilization of a slurry. More particularly, the invention pertains to a slurry excavating method which employs a slurry containing a water absorbing resin powder and which permits excavation of the ground or drilling a hole while preventing the so-called loose water phenomenon wherein the slurry is lost in gaps in the ground or cracks in a shuttered shale layer, fissile layer or the like.
2. Description of the Prior Art
For excavating the ground or drilling a hole in the ground through the use of a slurry, there have heretofore been proposed a continuous underground wall method, various piling methods, a slurry pressurized shield method and various boring methods. With such methos, a ditch (or hole) being drilled or a cutting area is filled with a slurry and a water sealing mud cake of slurry components is formed on the wall surface of the ditch or in the cutting area that makes contact with the slurry and, as a result of this, the pressure of the slurry acts on the natural ground to prevent crumbling of the ditch wall or cutting area. The slurry heretofore employed is produced by suspending and dissolving in water one or more kinds of clays, such as bentonite, natural or synthetic high molecular weight substances and potter's clay. The slurry is held in a state of good fluidity such as a viscosity of 5 to 50 cps. and a specific gravity of about 1.05 so as to facilitate its supply and recovery and subsequent steps, such as concrete placing and so on. On account of such high fluidity, when the nature of the ground being excavated or drilled is gravel or is cracked, imperfect mud cakes are formed in coarse gaps of the gravel or the cracks, resulting in what is called a loose or lost water phenomenon, whereby the slurry percolates downward through the surrounding soil in large quantities. A decrease in the slurry pressure by the lost water phenomenon in the ditch being drilled or in the cutting area leads to the crumbling of the ditch wall and pollution of surrounding underground water. Therefore, prevention of the lost water phenomenon is indispensable to the slurry excavating method and a variety of countermeasures have hitherto been proposed. One method that has been employed is to add to the slurry lost water preventive materials, such as cottonseeds, sawdust, pulp, chrisotile, mica and so forth. The kinds and concentrations of such materials are determined in consideration of the kind of slurry used, but these materials are defective in that they surface or precipitate and do not stably disperse in the slurry because they appreciably differ in specific gravity from the slurry.
Recently there has been proposed in Japanese Pat. Laid-Open No. 92508/76 a method that prevents the lost water phenomenon by adding to an excavating slurry water soluble high molecular weight substances having a mannose radical at its cis-position in combination with boric acid (salt) to thereby gelatinize the slurry containing the water soluble high weight compound.
With this method, however, since the property of a gel formed in the slurry varies with atmospheric or water temperature, or the nature of water, field work becomes complex. In addition, since the viscosity and specific gravity of the excavating slurry are confined within narrow limits as referred to previously, the quantities of the water soluble high weight material and a hardening agent added must be small. This reduces the quantity of the gel formed and decreases the gel strength and, consequently, the gel formed flows out through voids in the gravel, resulting in the effect of lost water prevention not being as effective as expected.